In an orthogonal frequency division multiple access (OFDMA) communications system, time-frequency resources of the system may be shared among a plurality of mobile stations (MS). A base station (BS) may assign time-frequency resource to MS using an assignment message, which may be transmitted as part of a control channel. To minimize control channel overhead, the BS may make persistent assignments, wherein the assignment message is transmitted to the MS to initially indicate the assigned time-frequency resource, and then the BS uses the assigned time-frequency resource for subsequent transmissions to or receptions from the MS.
These transmissions may be hybrid automatic repeat request (H-ARQ) transmissions of the same transmission, for subsequent transmissions of different transmissions, or for initial transmissions of different transmissions, or for initial transmissions of a series of transmissions. For example, in a voice over internet protocol (VoIP) system, the BS may make a persistent resource assignment to a MS consisting of a time-frequency resource with a period equal to 20 msec (a vocoder period). Then, the BS may use this resource for the first H-ARQ transmission of each VoIP transmission. Subsequent transmissions, if necessary, must be signaled.
The initially assigned time-frequency resource may be maintained by the BS for the MS until a timer elapses, a VoIP talk-spurt completes, a VoIP call completes, the BS determines a certain number of negative acknowledgements, the BS explicitly or implicitly de-assigns the assigned time-frequency resource, or so forth.
In a wireless communications system with fixed boundaries, the assigned time-frequency resource may be specified static number, such as a number representing the beginning of the assigned time-frequency resource. However, in some wireless communications systems, there are dynamic boundaries. For example, in a time division duplex (TDD) wireless communications system, a boundary between a downlink and an uplink may be dynamic. Similarly, in a half duplex frequency division duplex (H-FDD) wireless communications system, a boundary between two groups may be dynamic. In wireless communications system with dynamic boundaries, a persistent assignment made using a static number may become incorrect once a boundary changes. In such wireless communications systems, there is not currently a mechanism to support continuing a persistent assignment when a boundary change occurs. Thus, there is a need for assigning persistent resources in a dynamic manner to allow for changing boundaries.